The present invention relates to a one part primerless silicone hardcoat compositions comprising an aqueous/organic solvent silicone dispersion consisting essentially of colloidal silica, and a partial condensate of an organoalkoxysilane, in combination with an effective amount of an adhesion promoter, such as an acrylated or methacrylated polyurethane, or an acrylic copolymer, such as an acrylic polyol.
Prior the the present invention, as shown by Patel, U.S. Pat. No. 5,041,313, silicone hardcoat composites were made by a two part procedure by initially priming a thermoplastic substrate, such as a polycarbonate substrate, with a solution of a polyacrylic resin in a solvent blend, followed by the application of a silicone hardcoat composition. Goossens, U.S. Pat. No. 4,615,947, shows that a thermoset or thermoplastic acrylic polymer having a molecular weight of at least 15000 can be mixed with an organopolysiloxane to produce a primer layer on a thermoplastic substrate. The primer layer is used initially to increase the adhesion of a subsequently applied organopolysiloxane hardcoat.
European patent application 0439294A1 suggests that priming a thermoplastic substrate prior to the application of the silicone hardcoat is not necessary if a monomeric hydroxy acrylate such as 2-hydroxy ethyl methacrylate is added to the hardcoat mixture before it is thermally cured. However, the use of hydroxy acrylates in coating compositions has sometimes been restricted because of their toxicity, as taught in Chung, U.S. Pat. No. 4,486,504. It would be desirable therefore to be able to formulate one part heat curable silicone hardcoat compositions which can be directly applied in an environmentally safe manner onto a variety of thermoplastic substrates without the requirement of a primer.